The present invention relates to an organic glass which has a high refractive index and excels in other optical properties and so lends itself well for materials for optical parts such as lenses and prisms.
In the following description, the organic glass for optical parts according to this invention will be explained specifically but not exclusively with reference to lenses.
In the present disclosure, it is noted that unless otherwise stated, "parts" are given by weight.
It is also understood that unless otherwise specified, the term "urethane acrylate" used hereinafter refers to an urethane acrylate which may contain as the acid component not only acrylic acid but methacrylic acid as well.
Organic glass, being lighter in weight than inorganic glass, has attracted attention as a lens material for spectacles, and an organic glass of the type made of polymers of diethylene glycol bis(allyl carbonate)--hereinafer ADC for short, methyl methacrylate, etc. has been used to this end. However, this organic glass has a refractive index of 1.49-1.50, which is lower than that of inorganic glass (e.g., that of white crown glass is 1.523), so that when it is used as a lens material for spectacles for correcting visual power, the lens becomes thicker than that made up of inorganic glass, imparing the merits of being lighter weight, and imparing appearance as well. This tendency becomes more marked as the degree of the lens becomes strong. Thus, organic glass does not always lend itself well for a material for visual power-correcting lenses.
In order to overcome this problem, for instance, a copolymer composed mainly of a diallyl ester of biphenyl dicarboxylate has been proposed (Japanese Patent Laid-Open Publication No. 63-23908), but there is still left much to be desired in terms of a refractive index, impact resistance, etc.
In general, difunctional unsaturated compounds are likely to yield hard and fragile polymers, because they form a three-dimensional, crosslinked structure by polymerization reactions. In such cases, the introduction of a certain unsaturated compound into the crosslinked structure comes to mind (see, for instance, Japanese Patent Publication No. 62-50488). In the case of a biphenyl compound, however, this alone would make it difficult to improve impact resistance, because the degree of rigidness of the crosslinked structure is much higher.
In view of such situations as mentioned above, an object of this invention is to provide an organic glass for optical parts, which does not only possess a high refractive index but also excels in various physical properties, inter alia., impact resistance as well.